Energy related technologies such as fuel cells, batteries, gas sensors, etc. are often based on heterogeneous gas-solid or liquid-solid reactions, and require very good circulation of the reactants and reaction products.
These devices (fuel cells, batteries, gas sensors) are based on redox reactions and comprise electrodes which must therefore also permit good circulation of the reactants and reaction products.
These electrodes comprise in particular a catalyst deposited on one of the elements of the electrode.
To optimize the efficiency of this catalyst, nano-electrodes organized at the nanometric scale are increasingly advantageous for many applications.
This is because conventional catalyst deposition techniques are not generally suitable for obtaining three-dimensional structures which are perfectly controlled, neither in terms of size, nor in terms of catalyst dispersion.
To overcome this drawback, Choi et al. proposed, in “Pt nanowires prepared via a polymer template method: Its promise toward high Pt-loaded electrocatalysts for methanol oxidation”, Electrochimica Acta 53 (19):5804-5811, 2008 the use of a matrix to fabricate platinum nanowires which are then deposited on a substrate.
In this method, a polycarbonate matrix is fabricated, perforated in the thickness direction to form open holes on two opposite surfaces of the matrix.
It is in the holes of this matrix that the platinum catalyst is grown by electrochemical reduction of a platinum salt.
However, this method has a major limitation because it is necessary to deposit a dense, uniform and sufficiently thick layer of a conductive material on one of the faces of the matrix at which the orifices of the holes open.
It is necessary to deposit this layer to obstruct one end of the holes of the matrix and thereby allow the growth of the metal structures exclusively inside the holes of the matrix.
The matrix is then destroyed, leaving only the metal layer on which the metal structures (nanowires) (columns) are arranged vertically.
In fact, the dense and uniform metal layer, such as the one that is commonly deposited, that is a layer of gold, does not allow the proper circulation of the fluids required for the good circulation of the reactants and reaction products.
One solution, suggested by Choi et al., is to separate all the nanowires obtained from the metal layer and place them in suspension in a solution containing an organic binder, and then to deposit this suspension on a substrate which is generally nonporous.
However, this technique is not suitable for preserving the original nano-organization.
Other techniques serve to obtain metal wires on a porous substrate, but neither the size nor the dispersion of the wires can be easily controlled.
These techniques involve growing the nanowires on a platinum or titanium gauze or on carbon felts.
Such methods are described, in particular in Lee at al., “Growing Pt nanowires as a densely packed array on metal gauze”, Journal of the American Chemical Society 129 (35): 10634, 2007.